The invention relates to a process for utilization of waste heat from a high-temperature hood in the dryer section of a paper machine, as well as a suitable device for implementing the process.
This process and device is intended to improve utilization of the energy contained in the exhaust air from a high-temperature hood.
The dryer section of a paper machine consists of a steam-heated dryer and a high-temperature hood heated by steam or gas and located above the dryer. The dryer is generally operated with steam pressures between 1 and 10 bar, and the blow-air temperature of the high-temperature hood is usually between 250° C. and 700° C. In principle, utilizing the waste heat from the blow air of a high-temperature hood in stages is state-of-the-art. It mainly heats supply air and combustion air, as well as heating water and process water. DE 3501584 also describes a device with which the waste heat from the blow air of a high-temperature hood can be used to generate steam. Here, the condensate collecting in the dryer is brought from a steam separator into a heat exchanger for waste heat from the high-temperature hood, where it evaporates due to the energy content of the exhaust air from the high-temperature hood. Subsequently, the steam thus generated is fed again to the dryer.
This known heat recovery process has the disadvantage that the condensate fed through the heat exchanger must always be measured such that the condensate is guaranteed to evaporate completely in the exchanger or after any reduction in pressure. Thus, when controlling the flow of condensate through the heat exchanger it is essential to take the evaporating capacity of the heat exchanger into account; this leads to regulating problems if there are fluctuations in the temperature of the exhaust air from hood.